Power transmission



Aug. 26, 1941. R. c'. GRIFFITH 2,253,617

` f POWER TRANSMISION l Filed Nav. 1s, 19:58

' ATTORNEY Pafenfed Aug. ze, 1941 I UNITED STATE aznar?4 sum1 Powlm sIoN numana c. ausnahme men., am u Vickers Incorporated, Detroit,

tionoflllchlgan mampara- Appiication November 18, 1938, Serial No. 241,1z1 z claim. (ci. 12x-'151) This invention relates to power tons. particularly to those of the type comprising two or more fluid pressure energy Ydevices one of which may function as a pump and another as a iiuid motor.

The invention is particularly concerned with a transmission system adapted for operation of a reversible double-acting motor, for example, the operating ram of a hydraulic press, shear. punch. or the like. For certain classes of work such as metal drawing, punching, and shearing. mechani cal crank-operated presses have been widely used in the past due to their greater operating speeds. anditisonlywithinthepastfewyearsthathydraulic press speeds have approached the point where they can successfully compete with mechanical presses in this class of work.l

The usual mechanical press is controlled by a one-revolution clutch. This clutch is controlled from a lever or foot pedal in such a way thatv when the pedal is operated1 the press is started and' goesthrough one cycle, consisting of a.` forwardandaretumstroke,comingtorestatthe end of the return stroke if the pedal has in the meantime been released. 1f, however, the pedal is held in the starting position, the press will operate in continuously repeated cycles so long as the pedal is held there, and when the pedal is released the press will stop at the end of the next return stroke. Control systems for hydraulic presses are commonly ananged so that it is necesconstitute a reversible double-acting fluid motor, L although it will be understood that'other types oi sary to manually initiate each separate cycle? or if continuously repeated cycles are desired, it is necessary to operate a starting control to start the press in operation and-to later operatea stop-v ping control when it is desired operation. l

It is an-object of the present invention to provide an improved hydraulic transmission system of the class described wherein simple control means is provided for permitting either single cycle or repeated cycle operations from asingle 'control element which, when moved to one position, willstartI the system in operation either to terminate the Athrough one cycle or through repeated cycles, de-

pending upon how long the control element is maintained in the starting position.'

It is'a further object to provide a system of this character with improved emergency stopping mechanism which isV effective to stop the motor whether-it is on an advancing stroke .or on s return stroke and which emergency control may be effected by operation of a single lever in 'one direction regardless of whether the motor .is on its advancing or returning stroke.

description, reference being had to the siccom-A panying drawing wherein a preferred form of the present invention is clearly shown.

Inthedrawingthesingleflgureisadiagrammatic view of a power transmission system incorporating a preferred form of the present invention. l

Thepump il is adaptedtobedrivenbyaprlme mover such as an electric motor VI2 to withdraw f iuid from a tank I4 through a suction conduit I8 and deliver the same to a delivery conduit I8 having a conventional relief valve `2l for lay-passing lluid to the tank through a conduit 22 whenever a predetermined safe pressure is exceeded in the conduit il.

Theconduit il leads to the pressure portv 24 ot a pilot-operated four-way valve 28. The tank ports 28 of the valve 2l are connected by a conduit 3l to 'the tank. Cylinder P01125 32 and 34' connect by conduits I6 and 38 to the head and rod ends respectively of a cylindeil 4l. Within the cylinder 4l is reciprocably mounted a piston 42 having a rod 44 to which is attached a platen 46 of 'a hydraulic press. The cylinder 4I and piston 42 iluid motor including those ofthe rotary type may be equally suitable for use with thepresent invention, for example,l under conditions where alternately reversing rotary movement lmay bev required.

Interposed in the conduit 38 is a pressure responsive foot valve 4I of well-known construction comprising a spool normally held to the left in closed position by a spring 52 and adapted to be moved tothe right by pressure in the conduit Il transmitted through a conduit 54 to the left-hand lend of the spool 50. The valve 48 is preferably adjusted so that the pressurerequired to open the' same and which is produced in the rod end of cylinder 40 by the gravity load on the .piston 42 is sumcient to provide a' source of iluid for pilot control purposes. A check valve 56 permits free now through the conduit 38 into the rod end of the cylinder 40.

, 'Ihe pilot-operated tour-way valve 28 is provided with a spool Il having a land 60 which blocks the port 34 in center position and a land j l2 which is beveled oi! on'its opposite sides to trol connections 'I6 and 18 communicate with the bores 68 and 'I0 by means of adjustable restrictions 80 and 82 in parallel with which are a pair of check valves 84 and 86. Emergency control connections 88 and 80 communicate with the bores 68 and 10 directly, that is, without passing through therestrictions and check valves.

The spool 58 is provided with a shoulder 92 at its right-hand end which is adapted to engage a detent '94 pivoted at 96 in the valve body and spring-biased in a counterclockwise direction to the position shown in the drawing. A suitable control lever 98 is provided for swinging the detent clockwise to release the same from engagement with the shoulder 92.

For the purpose of normally controlling the pilot-operated valve 26, a four-Way pilot valve is provided having ports P, T, I and 2. The latter are controlled by a rotor |02 which is shlftable forty-five degrees clockwise from the position shown to transpose the connections through the valve. Port P is connected by a conduit |04 with the 'conduit 38 at a point between the cylinder 40 and the foot valve 48. Port T is connected to tank by a conduit |06. Ports 'I and 2 connect by conduits |08 and I|0 with the control connections 'I6 and 'I8 respectively.

The rotorv of pilot valve |00 is provided with a lever I|2fwhich may be controlled by suitable dogs ||4 and H6 carried by an extension rod I|8 secured to the platen 46. When the platen is in its uppermost position, the dog I|4 shifts the lever II2 and rotor |02 into the position shown in the drawing. When the platen reaches its lowermostposition the dog |'I6 contacts the lever I2 to shift the rotor |02 clockwise forty-five degrees and transpose the connections. The dog ||6 may be adjustably mounted on the rod ||8 and is adapted to be completely removed therefrom when it is desired to control the end point of the working stroke from the working pressure rather .than from the position of the platen 46.

For this purpose the rotor |02 is provided with a second lever |20 adapted to be operated 'by a piston |22 slidably mounted in a. cylinder |24 and' urged to the left by a spring |26. The left end of cylinder |24 connects by a conduit |28 with the conduit 36, a suitable shut-oli valve |30 being provided in the conduit |28. When, at the completion of aqworklng stroke, the pressure builds up to a sufficient value to overcome the force of the spring |26, the piston |22 moves to/y the right shifting the lever |20 and rotor |02 in a clockwise direction to transpose the connections through pilot valve |00 in the same manner as when the same is shifted by the dog I I6. The dog I|6 and the piston |22 thus constitute alternative means for shifting the pilot valve |00 at the completion of a working stroke.

For purposes of emergency control a second rotary pilot valve |32 is provided which is similar to the pilot v alve |00. The rotor |34 of valve |32 may be controlled by a'hand lever |36 whichV is biased by 'a spring |38 in a clockwise direction and maintained in its center position as shown b a stop pin |40.

Port P'of pilot valve |32 connects by a conduit |42 to the conduit 38 while port T connects by a conduit |44 tothe emergency control connection 88. Port 2 connects by a conduit |46 to the conduit 36 while port I connects by a conduit |48 to the emergency control connection 90.

In operation, assuming the parts to be in the position shown-Qin the drawing and that the motor I2 and pump I0 are operating, fluid is withdrawn from the tank I4 through the conduit I6 and delivered through conduit I8 to port 24 of valve 26 from which it, passes out port 28 and through conduit 30 to tank. The pump I0 is thus bypassed with negligible resistance.

The piston 42 is held stationary because the oil in the rod end of the cylinder 40 is trapped from escaping through the conduit 38 both by the foot valve 48 and by the land 60 in the four-way valve 26. 'I'hegplaten 46 thus remains stationary.

To start a cycle of operations, the lever 98 is moved clockwise to retract the detent 94. Since f pressure is maintained in the cylinder 10 through the conduit |04, ports P and 2 of valve |00, and

conduit I|0, the spool 58 shifts to the right at a v speed determined by the setting of the restrictor '80 which determines the rate at which oil can be discharged from the cylinder 68 at' the righthand end of valve 26. Fluid, of course, enters the cylinder 'I0 freely through the check valve 86.

With the spool 58V thus shifted to its right-hand position port 24 is placed in communication with port 32 and port 28 is placed in communication with port 34. Oil thus passes from conduit |8 through conduit 36 to the head end of cylinder 40 ports P- and I of valve I 00 and conduit |08 to the cylinder 68, thus shifting the spool 58 to the left at a speed determined by the setting of restrictor 82. Oil discharged from the cylinder 'I8 passes through conduit ||0, ports 2 and T of valve |00 and conduit |06 to the tank. With the spool 58 thus shifted to its leftmost position port 24 is placed in communication with port 34 and oil flows from conduit I8 through conduit'38 and check valve 56 to the rod end of cylinder 40., The piston 42 accordingly moves upwardly discharging oil from the head end of cylinder 40 through conduit 36, ports 32 and 28, and conduit 30 to tank. The same action ,takes place when the piston |22 is connected to cause shifting of valve |00 when a predetermined pressure builds up in line 36.

As the platen approaches its upper position, dog II4 contactslever |I2 to shift the rotor |82 counterclockwise into the position shown in the drawing. Pressure from conduit 38 is thus again transmitted through conduit I |0 to the cylinder l0, shifting spool 58 to the left.

If, in the meantime, the lever 98 has been released to position the detent 94 in the path of the shoulder 92, the s pool 58 will only shift as far as its center position, thus bringing the piston 42 to a stop and restoring the system to its starting condition previously described. If, however, the lever 98 .has not been released prior to the shifting of valve |00, the' spool 58 will shift all the way to the right, initiating a second cycle of operation identical to' that previously described.l Thus it is apparent that the piston 42 will start and complete one cycle of operations if the lever 98 is shifted clockwise and released before the cycle is completed, and that ifv the lever is not released, the piston 42 willcontinue to operate through repeated cycles until the lever than position by removal of the dog |3 and opening the valve |30.

If during any part of the cycle an emergency should arise necessitating immediate stopping or reversal of the piston 42, the Ilever |33 can be l0 operated counterclockwise to open connections through the pilot valve |32. `If the lever |33 be thus shifted while thepiston 42 is moving downwardly, it will be seen that communication is established from the conduit. (which is under lo pressure through conduit |43), ports 2 and T of valve |32, and conduit |44 to the connection 88. Since the spool 58 is in its right-hand position on the down stroke of piston 42, oily entering the cylinder 38 will shift the spool 33 toward 20 the left discharging oil from the cylinder." through connection 80, conduit |48, ports and P of valve |32 and conduit |42 to conduit 38.

'I'he conduit 38"is in communication with the v. l .tank while the spool 58 ls in its right-hand posi- 2s tion. As soon as the spool reaches its center position this communicationis blocked so that oil can no longer discharge from the cylinder I3 through the connections described. The piston 42 is thus brought `to rest substantially instanso taneously by shifting lever |33.

It will be notedthat during this emergency shifting of the spool 53, conduit `|33 is connected to tank and conduit |||I is connected to pressure in line 38. Inasmuch asthe communication of 35 conduits |08 and ||8 with the cylinders 33 and 13 is through the restrictors 33 and 32 it will be seen that only a limited quantity of oil entering the emergency connection 33 will be discharged to tank through the restrictor'33, the remainder 40 ,being effective to shift the piston 34. Likewise at the left end of valve 23, the pressure oil entering from conduit llt through restrictor 32 and discharged to tank through the connection 33 will be limited in quantity. Thus the'press is 4,5

brought to a stop on its working stroke by downward actuation of the lever |33. Y

If, on the other hand,'.the,press should be on a returning stroke and an emergency arise,

the lever |33 may be likewise shifted dovm- 50 wardlytoestablishthe same connectionsthrough the valve |32. .Under these conditions, the spool 53 bein'ginits leftmostposi lndtheline 33 being under pressure,foil fro this line will iiow through the conduit |42, ports P and of u valve |32 and emergency connection 33 to the cylinder 13. The spool 33 thus shifts to the right discharging oil from cylinder 33 through connection 33, conduit |44, ports T and 2 of valve |32 and conduit |43' to conduit Il which .is in n communication with the tank atthis time. Inasmuch as the lever 33 would normally have been I'released prior toshifting the lever |33, the detent 34 isinthepath of theshoulder 32 sothitttlmo` spool 33canonlyshifttothe rightasfar-asits u center position. During this 'rightward' shifting the communication of cylinder I3 withthe tank .through conduit III lsrestrictedbytherestrictor 32, while the pressure connection of cylinder 33 ugh conduit m is likewise restricted by the 10' alf Obviously the two levers |33 and 33 can be connected for operation fromv a single control element arranged in abutting relation'to -each lever so that the single element when shifted in one direction (clockwisel away from its neutral position will operate the lever 98 and when shifted in the opposite direction? away from neutral will actuate the lever |33. The springbiases acting on levers |33 and 33 will normally hold such control element inneutral position.

Likewise it will be understood that foot valve 43 may be omitted if it is desired to utilize a different means for supplying pressure iiuid to conduit- |II4 for operating the pilot circuits controlled by valve |33. For example, the beveling at land 32 may be made such as to vproduce sumcient back pressure in line I3 when spool I3 is centered to operate the pilot circuit, and the line V|34 may then be connected to line lI3 instead of line 38. 0n the other hand, an auxiliary source of pilot pressure independent of the main operating circuit may be utilized.

Whilethe form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might beadopted, all coming within the scope of the claims which follow. What is claimed is as follows:

1. In a hydraulic power transmission system the combination with a source of pressure fluid and a double-acting reversible fluid motor of a directional controlvalve having forward, neutral andreverse positions for controlling the flow ofl fluid' to the motor to respectively advance, stop and retract thev motor, a pilot motor for shifting the control valve, pilot control means. for causing 4 the control valve to shift between the forward and reverse positions at the completion of each stroke, a detent arranged in the path of move^ ment. of the control valve from reverse to fore ward position to hold the valve in neutral position, means for retracting said detent to start operation of the motor through repeated cycles of advancing andretracting strokes while said detent is held retracted, anda second pilot control means connected with said 'pilot motor and shiftable in a single direction'for causing shifting of said control valve in either direction ldepending on whether it lies in the forward or reverse posi, tion. f l

' 2.1nahydraulic poweronsystemthecomblnationwlthasourceofpressureilmd anda double-acting reversible fluid motor of a directional control valve having forward, neutral and reverse positions for controlling .the now of fluid to the motor to respectively advance, stop, and retract the motor, a pilot motor for shifting the control valve, pilot control means for causing control valve to shift between the forward-- reverse positions .at the completion of each stroke, a detent arrangcdin the path of movement ofQthe control valve from reverse to forwardpositiontoholdthevalveinneutralposi-` .able in a-aintle directionin a-mannerto shift the controlvalvein a'direction oppositeto that dictated bythe pilotcontrol means when the emergencycontrolmeanslsaetmted.

. Y .Hammam 

